1. Field of the Invention
This invention relates to a nickel-hydrogen storage battery with improved high-temperature performance and a process for producing the same.
2. Description of the Related Art
The recent development in electronics has promoted reduction in size and weight of electronic equipment, and the demand for storage batteries as a power source of the electronic equipment has been increasing. Accordingly, the storage batteries have been required to have higher capacities and longer lives.
In recent years, nickel-hydrogen storage batteries comprising a metal compound such as nickel hydroxide as a positive electrode and a hydrogen absorbing alloy as a negative electrode have been attracting attention as alkali storage batteries taking the place of nickel-cadmium storage batteries. The nickel-hydrogen storage batteries are characterized by the higher energy density than the nickel-cadmium storage batteries and their environment friendliness because cadmium is not used as a negative electrode.
JP-A-5-28992 proposes a nickel-hydrogen storage battery in which nickel is used as a positive electrode that is highly utilizable as an active material over a wide temperature range.
According to the disclosure, the utilization of the active material in high temperature is improved without impairing the utilization in room temperature by adding to the active material mainly comprising nickel oxide at least one compound of yttrium, indium, antimony, barium or beryllium. JP-A-5-28992 also describes addition of a cobalt compound to the nickel positive electrode and addition of potassium hydroxide and 10 g/l or more of lithium hydroxide to the electrolytic solution.
According to the present inventors"" study, however, it has turned out that nickel-hydrogen batteries having the conventional positive electrode undergo considerable reduction in capacity on repetition of charge and discharge cycles in high temperature. Addition of the conventional additives, such as the yttrium compound, to the active material and addition of lithium hydroxide to the electrolytic solution are still insufficient to produce effects in suppressing capacity reduction in high temperature.